import java.util.HashMap;
import java.util.Scanner;

public class TestDay22 {


    //升级
    public static void main1(String[] args) {
        //
        Scanner scanner = new Scanner(System.in);
       while (scanner.hasNext()){
           int n = scanner.nextInt();
           int HP = scanner.nextInt();
           for (int i = 0; i < n; i++) {
               int z = scanner.nextInt();
               if(HP < z){
                   //求最大公约数
                   int A = 0;
                   int B = 0;
                   int c = 0;
                   A = HP;//105
                   B = z;//100
                   while ((c=A%B)!=0){
                       //辗转相除法
                       A = B;
                       B = c;
                   }
                   HP += B;

               }else {
                   HP+=z;
               }
           }
           System.out.println(HP);
       }
    }
    //只出现一次的字符
    public static void main(String[] args) {
        HashMap<Character,Integer> hashMap = new HashMap<>();
        Scanner scanner = new Scanner(System.in);
        String str = scanner.nextLine();
        for (int i = 0; i < str.length(); i++) {
            //如果没有出现过就返回0再+1
            //如果出现过就返回当前出现次数再+1
            hashMap.put(str.charAt(i),hashMap.getOrDefault(str.charAt(i),0)+1);
        }
        for (int i = 0; i < str.length(); i++) {
            if(hashMap.get(str.charAt(i)) == 1){
                System.out.println(str.charAt(i));
                return;
            }
        }
        System.out.println(-1);
    }

}
